This invention relates to a method of measuring d.c. flux and a device therefor.
More particularly, the invention is concerned with a method and a digital displacement transducer apparatus for the measurement of a digital output which is related to the linearly displacement of a reference surface of an object.
A device which provides a digital output related to the displacement of a surface is a digital displacement transducer. It is desired to provide such a transducer to measure spatial displacement of approximately 0.004 inches (1/256 of an inch) of surface. One manner of providing a digital output related to spatial displacement is to provide an eight track magnetic tape or equivalent magnetic sheet and attach the tape to a reference surface of the object. The position of the reference surface could then be ascertained by reading coded information on the magnetic tape. For this purpose a stationary head would be used to read the coded information. In order to read the tape, it would be necessary to use a Hall probe or other equivalent d.c. flux measuring device; it would have to be used in the stationary head. While this technique is useful, it is quite costly. Hall probes are expensive, and they require flux condensing as small d.c. fields must be read.
In order to overcome the aforesaid problems and reduce the costs, the present invention proposes two embodiments to provide for the non-destructive read-out of the coded magnetic tape.
One embodiment is to provide a hard magnetic tape which is coded with magnetic information related to the displacement of a reference surface. A second soft magnetic tape is juxtaposed next to the hard magnetic tape and flux closed therewith. A magnetic field pulse is applied to the composite tape unit to change the magnetic stored information from a one or a positive state to a zero or negative state. The magnetic field has no effect on those already in the negative state. The magnetic field pulse is sufficiently strong to switch the information stored in the soft magnetic tape, but it is insufficient to switch the information stored in the hard magnetic tape. Therefore, the hard magnetic tape retains its coded information.
Another embodiment is to provide a single magnetic tape with coded information contained therein similar to the aforesaid hard magnetic tape. In this embodiment, the single tape also has eight tracks, although eight separate single track tapes can be used. A read head is provided for each track. Each read head includes a primary winding and a secondary winding. Use is made of the magnetic saturation characteristics of the read head to induce a large or small EMF into the secondary winding and provide a digital output.